This invention relates to the production of mercapto functional silanes. More specifically, it relates to the use of tertiary nitrogen-containing compounds to accelerate known reactions between haloalkyl silanes and thioureido compounds in the presence of ammonia or other alkaline compounds (such as sodium methoxide, amines, etc.) to yield mercapto functional silanes.
Silane coupling agents have become important compounds in industrial applications involving reinforcement of composites, such as filled plastics, and strong bonding between organic and inorganic materials. Mercapto functional silanes have been found especially useful as coupling agents in treating fillers for EPDM elastomers and in treating metal surfaces. "Silane Coupling Agents," a Dow Corning technical publication (copyright 1970, Dow Corning Corporation) and British Pat. No. 1,102,251 (Union Carbide), both incorporated herein by reference, describe such uses.
Mercapto functional silanes are typically produced by substitution of sulfur for halogen atoms in haloalkyl silanes, a favored method being reaction of a haloalkyl silane with a thioureido compound, such as thiourea, in the presence of ammonia. Although this method has the advantages of requiring no solvents and simple recovery of the product, there are disadvantages in that the reaction rate is slow and the recovery is only around 80%.
It has now been discovered that these disadvantages can be overcome by employing as an accelerator in the abovedescribed reactions certain tertiary nitrogen-containing compounds, including carbamides and diamines. These compounds have been found to accelerate the substitution reaction, allowing lower reaction temperatures, significantly descreasing the reaction time and increasing the yield of pure mercapto functional silanes to around 90% or more.